CONSTRUCTION OF A PROTOTYPE SOLAR BOILER
CHAPTER ONE INTRODUCTION
Energy is considered a prime agent in the generation of wealth and a significant factor in economic development. The importance of energy in economic development is recognized universally, and historical data verified that there is a strong relationship between the availability of energy and economic activity (Soteris, 2004). Although in the early seventies, after the oil crises, the concern was on the cost of energy, however during the past two decades, the risk and reality of environmental degradation have become more apparent. The growing evidence of environmental problems is due to a combination of several factors, since the environmental impact of human activities has grown dramatically (Soteris, 2004). This is due to the increase of the world population, energy consumption and industrial activities. Achieving solutions to the environmental problems that humanity faces today requires long term potential actions for sustainable development. Renewable energy resources appear to be one of the most efficient and effective solutions.
Of all the renewable sources of energy available, solar thermal energy is the most abundant one and is available in both direct as well as indirect forms. The Sun emits energy at a rate of 3.8 x 1023 kW, of which, approximately 1.8 x1014 kW is intercepted by the earth, which is located about 150 million km from the sun. About 60% of, this amount reaches the surface of the earth. The rest is reflected back into space and absorbed by the atmosphere. About 0.1% of this energy, when converted at an efficiency of 10% would generate four times the world‟s total generating capacity of about 3000 GW(Mirunalini, et al.,2010). It is also worth noting that the total annual solar radiation falling on the earth ismore than 7500 times the world‟s total annual primary energy consumption of 450 EJ (Mirunalini, et al., 2010). The annual solar radiation reaching the earth‟s surface, approximately 3,400,000 EJ,
is an order of magnitude greater than all the estimated (discovered and undiscovered) non- renewable energy resources, including fossil fuels and nuclear energy ( Mirunalini et al. , 2010). However, 80% of the present worldwide energy utilisation is based on fossil fuels.
World demand for fossil fuels (starting with oil) is expected to exceed annual production, probably within the next two decades (Mirunalini et al., 2010). International economic and political crisis and conflicts can also be initiated by shortages of oil or gas. Moreover, burning fossil fuel releases harmful emissions such as carbon dioxide, nitrogen oxides, aerosols, etc. which affect the local, regional and global environment. By means of different mechanisms, solar radiation may be converted into other forms of energy, such as photovoltaic conversion into electrical energy, photochemical conversion into chemically bound energy, and photo thermal conversion into heat. The heat converted from solar radiation, is well suited to provide domestic hot water and space heating. In most parts of the world, the yearly solar radiation received by a single family house is several times greater than the energy needed for domestic hot water and space heating( Mirunalini et al., 2010).
For many years, solar domestic hot water (DHW) systems have gained great attention due to their considerable energy conservation, environmental protection and relatively good economy. The purpose of using a solar DHW system is to convert the solar radiation into thermal energy, and then to use it for domestic hot water heating, thus reducing the over dependence on and consumption of conventional energy. Recently, environmental issues have led to an even greater interest in solar DHW systems. There are several fundamental conditions that make solar DHW systems very different from conventional fossil-fuel systems. Firstly, the power density of solar radiation is relatively low and the collector has to cover a large area. Thus, the solar DHW systems cannot be as compact as conventional
units. Secondly, the solar radiation varies considerably during the day, in the course of a
year and between different locations. Therefore, the solar energy received by a collector is an irregular function of time and location, and the power output of the collector cannot be controlled in the same way as conventional heating systems. Consequently, heat storage and auxiliary energy are required to match the supply to the load.
There is a strong consensus among climate scientists that the environmental problems now observed is caused by human activities targeted to meeting our energy demand, especially the combustion of fossil fuels. When oil, gas, or coal are burned to generate electricity or provide heat, the products of the combustion which include carbon dioxide and nitrous oxide, lead to global warming and acid rain deposition, respectively . The expected impacts of global warming include sea-level rise flooding of coastal areas increased frequency and severity of floods, draughts, storms, and heat waves, reduced agricultural production, massive species extinction, and the spread of vector-borne diseases such as malaria and dengue fever (Christopher and Homola, 2006). Thus, the manners in which we produce and consume energy (conventional way) are to a large extent responsible for this impending environmental problem (Intergovernmental Panel on Climate Change (IPCC), 2001).
According to Christopher and Homola (2006), rising economic losses due to weather- related disasters are part of a trend being linked to climate change. The World Health Organization estimates that climate change is already responsible for 150,000 deaths annually (Christopher and Homola, 2006).
Domestic hot water use again represents a large proportion of domestic energy need. This energy need accounts for approximately one third of the total annual energy consumption for domestic purposes and therefore a greater portion of the family income is spent on
domestic hot water (Retscreen International, 2004).
This research involves the design, simulation and construction of a prototype solar boiler
The design method employed is the simulation based method, where mathematical models for the determination of the system design parameters and characteristics were coded into a computer programme using the Matrix Laboratory (MATLAB) software in a manner that represents the conceptual design of the system.
The effects and sensitivity of the system design parameters on the collector heat removal factor were studied through programmes codes written in MATLAB in order to determine the size of the various components of the collector that will give better performance.
The system performance was simulated using the Transient Systems Simulation (TRNSYS) software for recommended average days of the months. The system was then constructed based on the adopted system configuration and components‟ sizes obtained from the studies. The performance of the system was then experimentally determined and the results obtained from the test were compared with the simulated results in order to validate the formulated model used for the performance simulation.
The aim of this research is to design and construct a prototype solar boiler
The specific objectives are:
- To carry out a parametric study on the effect and sensitivity of the tilt angle, , number of glasing , , absorber plate thickness, , collector tube diameter, and collector tube centre to centre distance, , on the objective function which is the percentage expression of the heat removal factor, , using Matrix Laboratory (MATLAB) programming language.
- To predict through simulation using TRNSYS, the annual performance of the system.
- To validate the predicted system performance through
- To estimate the cost
1.5 Significance of the Research.
Environmental concerns about global warming, local pollution and reduction of over dependence on conventional energy source for domestic hot water need in Nigeria, is the primary impetus for this research. This research would provide alternative way to providing hot water for domestic use in various homes. It also has the potential of reducing family utility bills and thereby improving family savings.